1. Field of the Invention
The present invention relates to a method for dehydrogenation, which comprises selectively oxidizing hydrogen present in a gas mixture formed at the time of dehydrogenation of a hydrocarbon to produce a dehydrogenated hydrocarbon.
2. Discussion of Background
A process for producing a dehydrogenated hydrocarbon by dehydrogenation of a hydrocarbon, has been disclosed in many literatures. For example, a process for preparing styrene by dehydrogenation of methylbenzene is industrially practiced by means of an iron-type catalyst. However, a dehydrogenation reaction is usually subject to a restriction of equilibrium, whereby it is difficult to attain a good yield. Further, the dehydrogenation reaction is an endothermic reaction, and if the reaction is carried out by an insulated reactor, the reaction temperature decreases as the reaction proceeds, whereby it is difficult to obtain the desired product in good yield.
Under these circumstances, some methods have already been proposed. For example, UK Patent No. 1,404,641 discloses a process and a catalyst for selectively oxidizing hydrogen in a gas mixture comprising unreacted methylbenzene, styrene and hydrogen after the dehydrogenation of ethylbenzene. This method is effective for the preparation of styrene, but A-type zeolite or alumina having platinum supported thereon is used as a catalyst for selective oxidation of hydrogen, and its performance is not necessarily satisfactory.
Also U.S. Pat. No. 4,565,898 discloses a method of using a catalyst having e.g. platinum tin and lithium supported on alumina for a similar process. However, this catalyst is supported also on alumina, and its performance is not fully satisfactory.
Further, Japanese Unexamined Patent Publications No. 89945/1983 and No. 298678/1994 disclose a method for selectively oxidizing hydrogen in a gas mixture comprising styrene, ethylbenzene and hydrogen, formed by the dehydrogenation reaction of ethylbenzene, by means of a catalyst containing tin oxide, or tin oxide and an alkali metal. This catalyst is noteworthy as a catalyst employing no platinum, but its performance is not necessarily adequate.
EP-A-0336622 discloses a similar process using a catalyst having palladium carried on tin oxide. However, according to this process, there was a problem of by-producing benzene and toluene and losing ethylbenzene and styrene.
As described above, conventional catalysts are not satisfactory in their performance as catalysts for selectively oxidizing hydrogen in a gas mixture comprising an unreacted hydrocarbon, a hydrogenated hydrocarbon and hydrogen, formed by the dehydrogenation reaction of a hydrocarbon.